Access Violation----Why is that?

[stealwings]

I have implemented a binary search and some other functions to my code, when I compile it, it gives me no error, but when I run it, it gives me an Access violation, why? Can some one explain me plz. Thanks in advance.

// SpanishBreakPredict.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <iostream>
using namespace std;
#include <fstream>
using std::ifstream;
using std::ofstream;
#include <stdio.h>
#include <cstdlib>
#include <string>
#include <stdlib.h>
#include <iomanip>
#include <vector>
#define MAXLENGTH 1000


int wmain(int argc, wchar_t * argv[], wchar_t *envp[])
{
	char WordCount[MAXLENGTH];		//Temp array to save input file words for lenght calculation
	char MyWord[MAXLENGTH];			//Temp array to save input file words.
	char MyStandard[MAXLENGTH];		//Temp array to save the standard words list
//	vector<string> MyWords;			// Vector to hold input file.
//	vector<string> Standard;		// Vector to hold Text-normalization-phrases
	ifstream CountStandard;
	ifstream CountInput;
	ifstream ReadWord;
	ifstream ReadStandard;
	ofstream WriteWord;

/**********************To get number of characters of each line****************************/
	int StandardSize=0;
	CountStandard.open("Standard.txt");
	while(!CountStandard.eof()&&CountStandard.getline(WordCount, MAXLENGTH))
	{
		StandardSize++;
	}
//	cout<<StandardSize<<endl;
	CountStandard.close();
	vector<string> Standard(StandardSize);
	int InputSize=0;
	CountInput.open("file.txt");
	while(!CountInput.eof()&&CountInput>>WordCount)//CountInput.getline(WordCount, MAXLENGTH))
	{
		InputSize++;
	}
	cout<<InputSize<<endl;
	vector<string> MyWords(InputSize);

/**************************************************************************************/
	WriteWord.open("file.dat",ios::app);
	if(!WriteWord.is_open())
	{
		cerr<<"couldn't create file"<<endl;
		exit(1);
	}
	ReadStandard.open("Standard.txt");	
	if (!ReadStandard)
	{
		cerr<<"Standard text file not found."<<endl;	
		exit (1);
	}
	
	
	while(!ReadStandard.eof())						//read the file till reaches the end.
	{

		ReadStandard.getline(MyStandard,MAXLENGTH);	  // read a line from the file.
													 //	(one line is a phrase)
		Standard.push_back(MyStandard);	//push the phrase into the vector "Standard";
		
	}												//read standard words over
	/*for(unsigned i=0; i<Standard.size();i++)
		{
			cout<<Standard[i]<<endl;
		}*/
	ReadStandard.close();//close the file handle;


	ReadWord.open("file.txt");
	if (!ReadWord)
	{
		cerr<<"input file not found please ensure it exist."<<endl;
		exit (1);
	}
	
	
	while(ReadWord>>MyWord)
	{
	//	cout<<MyWord<<endl;	
	//	ReadWord>>MyWord;
	//	ReadWord.getline(MyWord,MAXLENGTH);
		MyWords.push_back(MyWord);	
	}
   
/*******************************To print holding words of vector**********************/
/*	for(int i=0; i<MyWords.size(); i++)
	{
		cout<<MyWords[i]<<endl;
	}*/
/**************************************************************************************/
	ReadWord.close();
	WriteWord.close();

/**************************************************************************************/
/*					SEARCH AND COMPARE, THEN REPLACE IF MATCH IS TRUE.                */
/*                        Note: This part does a linear search						  */
/**************************************************************************************/
/*	for(unsigned i=0;i<Standard.size();i++) 
	{
			
		for(unsigned j=0;j<MyWords.size();j++)  //each MyWords compare to the Standard 
												//and see if it is in the standard vector
		{
			string::size_type FoundAt=MyWords[i].find(Standard[j]);
			while( string::npos != FoundAt )
				{
					MyWords[i].replace( FoundAt, Standard[j].length(),Standard[j]+"/");
					//cout<< MyWords[i]<< endl;
					FoundAt = MyWords[i].find( Standard[j], FoundAt + Standard[j].length() );
				}
		
			//if(MyWords[i]==Standard[j])			// if it equal to one of the words in the standard vector 
			//	MyWords[i]=MyWords[i]+"/";			// add the slash to the end;
		}
		
	}*/

	
/*********************************************************************************************/
/*									BinarySearch 											 */
/*********************************************************************************************/
int first=0, last, mid;
while(Standard[first]<=Standard[last])
{
	Standard[mid]=Standard[(first+last)/2];
	for (int i=0; i<MyWords.size(); i++)
	{
		if(MyWords[i]<Standard[mid].substr())
			first=mid+1;		

	}
}
/***********************************Create output file****************************************/
/*	for(unsigned j=0;j<MyWords.size();j++)		// for each word in MyWords vector  
	{
		WriteWord<<MyWords[j]<<endl;			// write it to the destination file
	}
	WriteWord.flush();							// flush the memory to ensure all is written to the file
	WriteWord.close();	*/						// close the write file handls
	return 0;
}

THAT IS MY CODE AND THIS IS THE PART THAT IS GIVING ME TROUBLE

int first=0, last, mid;
while(Standard[first]<=Standard[last])
{
	Standard[mid]=Standard[(first+last)/2];
	for (int i=0; i<MyWords.size(); i++)
	{
		if(MyWords[i]<Standard[mid].substr())
			first=mid+1;		

	}
}

[stealwings]

Sorry for the trouble, I already realized that it was a logical problem, it is solved, but I got this new problem, I have the part of the code as follow:

int first=0;
int last= StandardSize-1;
int mid=(first+last)/2;
//cout<<MyWords.size()<<endl;
	for (int i=0; i<MyWords.size();i++)
	{
		while(first<=last)
		{
			if(MyWords[i]>Standard[mid].substr())
				first=mid+1;
			else if(MyWords[i]<Standard[mid].substr())
				last=mid-1;
			else 
				cout<<Standard[mid]<<endl;
		}
		cout<<"Not found"<<endl;
		return -1; 
	}

it gives me an infinite loop of blank spaces, why?